1. Field of the Invention
This invention relates, in general, to wrapping and sealing with a thin film material and, more specifically, to wrapping and sealing stacks of printed sheets with a plastic film.
2. Description of the Prior Art
High speed printers, duplicators, and copiers are often required to produce copy sheets which are arranged in stacks. The stacks of sheets may consist of collated complete documents from the printer-copier, a fixed quantity of similar sheets, or any other multiple sheet stack which should be kept together.
Keeping such stacks of sheets together has taken many forms according to the prior art. Stapling, binding, wrapping, and stitching are but a few of the methods used to maintain the integrity of the stack once it leaves the output tray, tote, or hopper of the printer. Another desirable arrangement is to wrap a plastic film around the stack and seal together the film layers so that the sheets are neatly held in register with one another. Plastic wrapping offers the advantages of providing an impressive looking cover, see through capability for ease in address reading, and the ability to be mailed or shipped directly from the printer without further material and labor consuming operations.
While plastic wrapping and sealing apparatus has been known in the prior art, such apparatus is not ideally suited to applications involving high speed printers and copiers for various reasons. Therefore, it is desireable, and it is an object of this invention, to provide plastic wrapping and sealing apparatus which is specifically suitable for use with high speed printers and copiers, particularly with respect to the size and speed of the wrapping and sealing apparatus. It is also an object of this invention to provide a sealing arrangement which monitors the heat applied to the seal area according to a new and advantageous arrangement not known according to the prior art.
Several U.S. patents have been examined to determine the state of the prior art relative to the inventive concepts contained in this application. Expired U.S. Pat. No. 3,191,356, issued June 29, 1965, illustrates a wrapping and sealing machine which is somewhat similar to some aspects of the present invention. However, the apparatus of the referenced patent requires two stages or stations to seal all the edges of the package rather than sealing the edges simultaneously at the same section, thereby requiring valuable machine space and time. It is also noted that the parallel sides of the package according to the reference are sealed and the excess plastic is cut-off, unlike the present invention. Other differences between this reference and the present invention include the paper handling capabilities, the cut-off seal mechanism, and the manner in which the heat applied to the seal area is controlled.
U.S. Pat. No. 4,509,314, issued on Apr. 9, 1985, discloses a machine to band wrap a plurality of boxes with a plastic material. This reference uses a special lower feed mechanism which permits the use of a single roll of wrapping material. It is noted that the present invention differs from this reference because, among other differences, this reference does not seal the sides of the stack of boxes, does not lend itself to moving stacks of sheets into engagement with the plastic material, and uses a very different sealing and cut-off system.
U.S. Pat. No. 3,849,968, issued Nov. 26, 1974, discloses a packaging system which can seal a plastic wrap around sheets of paper. However, the cutting or severing of the plastic wrap is not performed during the sealing operation but rather at a separate location and in a different step of the process. Additionally, the sealing system is considerably different than that of the present invention.
Although the referenced patents show some similarities to certain separate features of the present invention, they do not provide the ability to quickly wrap a stack of sheets from a printer or copier within a relatively small enclosure. None of the references use or teach a sealing arrangement similar to that in the present invention, nor do they disclose the heat regulation system used in the present invention.